1. Field of the Invention
This invention relates to an image transferring sheet which is a combination of a thermally bonding sheet and a developer sheet superposed with each other and wherein the developer sheet is readily released from the thermally bonding sheet while transferring a developer layer of the developer sheet to the thermally bonding sheet. The invention also relates to a fabrication method thereof.
2. Description of Related Art
Color image formation apparatus of the type making use of a photo-sensitive and pressure-sensitive medium which has in the surface layer microcapsules containing a dye precursor, a photocurable resin and a photopolymerization initiator, and a developer medium having in the surface layer a material, or a so-called developer, capable of reaction with the dye precursor in the microcapsules for color development are known. In this apparatus, light is irradiated on the photo-sensitive and pressure-sensitive medium according to imagewise information to cure the photocurable resin irradiated with the light. Thereafter, the developer medium is superposed on the photo-sensitive and pressure-sensitive medium and pressed, so that non-cured microcapsules are broken to cause the dye precursor therein and the developer in the developer medium to react thereby forming a color image on the developer-bearing surface. This type of apparatus is known, for example, as shown in Japanese Laid-open Patent Application No. 173981/1986.
According to the apparatus described above, the color image can be formed on the developer medium, but it is not possible to form images on ordinary paper such as post card, cloth, plastic films and the like. In the case where it is positively intended to form images on post card or cloth, an image is formed on the developer medium, after which it may be possible to fix the image on the medium such as post card or cloth by bonding. However, this is not favorable because the medium increases in thickness with an increasing weight.
We developed and proposed in Japanese Laid-open Patent Application No. 206092/1989 a method for forming an image wherein the developer layer-bearing surface of a developer medium on which an image has been formed and the thermoplastic resin-bearing surface of a thermally bonding sheet comprised of a sheet substrate and a thermoplastic resin layer formed on the substrate are superposed and hot-pressed. After cooling, the support of the developer medium is released to transfer the developer layer (image layer) alone of the developer medium to the thermally bonding sheet. Subsequently, the thermally bonding sheet on which the developer layer has been transferred is bonded to an image-forming material such as post card or plastic film, thereby forming the image on the image-forming material.
In this method of the prior application, the thermally bonding sheet is bonded to the surface of the image-forming material along with the developer layer having been transferred, so that the flexibility of the image-forming material is impeded by the influence of the sheet substrate of the thermally bonding sheet. In order to form an image on an image-forming material, such as cloth, whose flexibility should be kept, other methods have been proposed, for example, in Japanese Laid-open Patent Application No. 3390/1990 and Japanese Laid-open Utility Model Nos. 10062/1990 and 10063/1990.
In these methods, while bonding forces among the sheet substrate of the thermally bonding sheet, the thermoplastic resin layer, the developer layer of the developer medium and the image-forming material are taken into account, the sheet substrate of the thermally bonding sheet which has been bonded to the image-forming material along with the developer layer is separated from the image-forming material. It will be noted that the transfer of the developer layer alone to the thermally bonding sheet is made in the same manner as in the foregoing methods.
However, these methods are disadvantageous in that depending on the type of thermoplastic resin used in the thermally bonding sheet, the manner of the hotpressing, the size of the thermally bonding sheet and the size of the developer medium, the transfer of the developer layer alone of the developer medium to the thermally bonding sheet may not proceed satisfactorily.
For instance, as shown in FIG. 6, when a thermally bonding sheet 22 is larger in size than a developer medium 21, an EVA resin having a softening point of 80.degree. C. to 85.degree. C. is formed on a sheet substrate 23 as a thermoplastic resin layer 20 in a thickness of 50 .mu.m and a heat roller having a line pressure of 1 kg/cm at 140.degree. C., the hot-pressed sheets are in such a state as shown in an enlarged section view of FIG. 6. More particularly, the thermoplastic resin 20 is melted down at the side of a support 21a of the developer medium 21, whereon a developer layer 21b is coated, so that the support 21a is unable to separate easily.